1. Field of the Invention
The present invention relates to mat materials and an exhaust gas treatment device.
2. Discussion of the Background
In proportion to the dramatic increase in the number of automobiles in the present century, the amount of exhaust gas from the internal combustion engines of the automobiles has also grown steadily. Particularly, various substances contained in the exhaust gas from diesel engines may cause pollution, thereby having a severe impact on the global environment.
Under such circumstances, various exhaust gas treatment devices have been proposed and put into practical use. Generally, exhaust gas treatment devices have a cylindrical member (casing) halfway through an exhaust pipe connected to an exhaust gas manifold of an engine and an exhaust gas treatment body having inlet and outlet opening surfaces for exhaust gas and forming a multiplicity of fine air holes inside the cylindrical member. Examples of the exhaust gas treatment body include a catalyst carrier and an exhaust gas filter such as a diesel particulate filter (DPF). With the above structure, the application of, e.g., the DPF permits fine particles to be trapped in the surrounding walls of air holes so that they are eliminated from exhaust gas, while the exhaust gas is exhausted from the outlet opening surface of the gas treatment body after entering through the inlet opening surface thereof.
Generally, a holding seal material is provided between the exhaust gas treatment body and the casing. The holding seal material is used to prevent breakage caused by a collision between the exhaust gas treatment body and the casing during vehicle operations and a leakage of exhaust gas from a gap between the casing and the exhaust gas treatment body. In addition, the holding seal material serves to prevent the dropping off of the exhaust gas treatment body due to the pressure of exhaust gas. Moreover, the exhaust gas treatment body is required to be held at high temperatures so as to maintain its reactivity, and the holding seal material is required to have a high heat insulation property as well. As a material satisfying these requirements, a mat material containing inorganic fibers such as alumina-based fibers is provided.
This mat material is wound around at least a part of an outer peripheral surface other than the opening surfaces of the exhaust gas treatment body and serves as the holding seal material by making its ends fitted or taped together so that the mat material is integrated with the exhaust gas treatment body. Then, the integrated product is press-fitted into the casing to thereby form the exhaust gas treatment device.
Note that the mat material contains a large amount of fine inorganic fibers and the inorganic fibers are exposed at the surface of the mat material. Such inorganic fibers may cause operating environments to be deteriorated. For example, at the time of handling the mat material, i.e., when an operator winds the mat material on the exhaust gas treatment body to manufacture the exhaust gas treatment device, these inorganic fibers are easily scattered to the surrounding area.
In order to alleviate the scattering problem of inorganic fibers at the time of handling the mat material, there has been proposed a mat material having resin films on its front and rear surfaces (see Japanese Patent Application Nos. 8-61054 and 2003-293756). The contents of Japanese Patent Application Nos. 8-61054 and 2003-293756 are incorporated herein by reference in their entirety.